Method for cracking oils in vapor phase



Jan. 17, 1939. C, KEN-Hy JR 2,143,917

METHOD FOR CRACKING OILS IN VAPOR PHASE ATTORNEY Jan, 17, 1939. P. c.KEITH, JR 2,143,917

METHOD FOR CRACKING OILS IN VAPOR PHASE Original Filed Deo. l, 1928Sheet's-Sheet 2 lNvENToR PERCY C. KEITH JR.

ATTORNEY Jan. 17, 1939.. p. c, KEITH, JR 2,143,917

METHOD FOR CRACKING OILS IN VAPOR PHASE Original Filed Dec. l, 1928 3Sheets-Sheet 3 g N N OOOGOOOO T122 "rs ATTORNEY Patented Jan. 17, 1939UNITED STATES PATENT GFFIQE METHOD FOR CRACKING OILS IN VAPOR PHASEPercy C. Keith, Jr., Peapack, N. J., assigner', by

mesne assignments, to Gasoline Products Company, Inc., Newark, DelawareN. J., a corporation of 3 Claims.

This invention relates to the pyrogenesis of petroleum oils and is adivision of application Serial No. 323,005 led December l, 1928 whichhas noW matured as Patent 1,972,149. The infiV Vention will be fullyexplained in the following description and accompanying drawings inwhich:

Fig. l is a diagrammatic representation of a preferred embodiment ofapparatus in which my l process may be carried out;

Fig. 2 is a diagrammatic representation oi an alternative form;

Fig. 3 is a Vertical Section through a form of apparatus which may beemployed in conjunction With my process;

Fig. 4 is a cross section taken on the line 4-4 of Fig. 3; and i Fig. 5is a side elevation with parts in section of a form of apparatusemployed in conjunction with my process and with the apparatus shown inFigs. 3 and 4.

The pyrogenesis of petroleum oils for production of oils of lowerboiling point is carried out by heating crude petroleum, or such of itsdistillates r as may economically be utilized in this manner,

to cracking temperatures with or without pressure. The fractionintermediate kerosene and lubricating oils known as gas oil isfrequently utilized for this purpose because of its lesser market value,although kerosene, lubricating oil fractions and fuel oils are alsoemployed at times. The fractions so employed are composed of an extendedrange of compounds as indicated by the range of molecular weights andboiling points. The conglomerate of compounds is subjected to crackingconditions until a certain quantity of material falling within a desiredboiling range is produced. Simultaneously with the formation of thisproduct, or products, materials are produced which do not fall withinthe desired range, for example, when cracking to produce a substantialproportion of gasoline which is a product composed of a large Variety ofdiierent hydrocarbon compounds, there is simultaneously produced aquantity of tarry and coky materials. Some elements of a conglomeratestock, for reasons which will be given more fully later, requirecracking to a degree less than others, and because of the fact that thestock as a Whole is subjected to the same conditions the crackingreaction will be carried too far in the case of some of the constituentsof the stock in order to secure the desired quantity of material of apredetermined boiling point range and with the resultant formation ofcompounds which do not fall Within the said range or which aredeleterious to the operation, for reasons which will be more fullypointed out. The different cracking rates of some oi the constituents ofthe stock tend to accentuate the condition referred to above. I havediscovered that a fundamental increase in the eiiiciency of the crackingprocess may be obtained by separating the cracking stock into a numberof distinct fractions of different .boiling point ranges and thereaftercracking the individual fractions so i generated. I prefer to obtain asnearly as possible, having regard to the conditions imposed by practice,a number of charging stocks all the constituents of each of which willrespond in the same degree to the conditions to which each of the stocksis subjected. I preferably apply to each such fraction the degree oftime, temperature, and/or pressure necessary to its optimum conversioninto desired products. These conditions may in any case be determined bypreliminary tests. Thus, when conditions have been established by suchtests as to yield the same quantity of desired end products from aseries of segregated fractions as is obtainable from crackingconglomerate stock the concomitant loss in gas and/or tarry or cokymaterials is diminished, or for an equivalent loss the yield of thedesired end products is relatively increased.

My process is applicable generally in the pyrogenesis of petroleum oilsto produce lower boiling i point oils, as, for example, cracking toproduce either gas, gasoline, kerosene, gas oil or lubricating oil fromstocks of respectively higher boiling point.

In the ideal embodiment of my process the stock is segregated into aplurality of charging stocks of such character that under the conditionsof heat, time, and pressure imposed cracking of the various individualcompounds composing the fraction will take place at substantially thesame rate. However, the limitations imposed by practice requiresegregation into .smaller number of stocks than in the ideal method andI therefore segregate into an appropriate number of charging stocks andsubject each. of such stocks to optimum conditions for the particularsegregate.

I have discovered that in high molecular Weight hydrocarbons of straightchain structure the initial scission on cracking frequently occursadjacent the center of the molecular chain. In one application in myprocess I aim to obtain by cracking the products of rst scission of themolecule, and I therefore prepare charging stocks which upon theirinitial scission yield products which ,fall within the range of physicalcharacteristics of the material desired to be obtained. Thus in the caseof gasoline I may proceed by dividing my charging stock into a number offractions each of which has a molecular weight substantially twice thatof a constituent of gasoline, then by cracking the stocks to the extentof one scission I obtain a number of products whose molecular weightsfall within the range of molecular weights of the constituents ofgasoline. In cases in which the original charging stock containsconstituents so heavy that the products of their initial scission willnot fall within the range o-f physical characteristics of the desiredproducts, these constituents may be separated from the remainder of theoriginal charging stock, as by distillation, 'and treated in one of twoways; i. e. (l) by segregating them from one another as by distillationinto individual fractions and then subjecting each segregated fractionto such conditions as will produce from eachl segregated fraction aproduct which will yield, upon refractionation, products which may bedecomposed as above into gasoline constituents. This procedure enablesme to separate unsaturated constituents to a degree and to then subjectsuch fractions to appropriate treatment. (2) In View of the limitationsof practice I may subject the entire heavier conglomerate cut tocracking conditions best suited to obtain the maximum yield of productswhich can be segregated into charging stocks of the nature described andcracked in the manner above set forth so as to yield gasolineconstituents.

Alternatively, I may prepare a number of fractions of charging stock,including some which cannot be converted by a single scission adjacentthe center of the molecule into products falling within the desiredrange, and subject each such fraction to the degree of time, temperatureand pressure necessary to its conversion into products of the desiredboiling point range. I may, however, in such cases crack each suchfraction to yield a cracked material having a position with respect tothe average molecular weight of the series of cracked materials obtainedwhich corresponds to the position held by the parent fraction withrespect to the other members of the parent series.

In addition to the foregoing I may make a further separation based onchemical characteristics. rIhus, I may separate the original crackingstock into twof fractions, one containing a preponderance of saturatesand the other containing a preponderance of aromatics and unsaturates,as, for example, by the application of selective treatment with liquidsulphur dioxide. These individual products may thereafter be separatedeach into products of different boiling point ranges to be separatelycracked as hereinabove described. Alternatively, the fractions ofseparate boiling point ranges may be rst prepared and each thereafterseparated into fractions of different chemical characteristics, as, forexample, by treatment with liquid sulphur dioxide.

In any event, where several fractions of the original charging stock areprepared, as by distillation, the decomposition products from theseveral fractions will preferably have average molecular weights Whoseratio to each other is approximately the same as the ratio of molecular'weights of the parent fractions. For example, in cracking gas oil toproduce gasoline the gas oil may be segregated by fractionation into aseries of several cuts, each of which has of constituents boiling withina different 50 F. range. The average molecular weights of thesefractions are in some ratio to their boiling points, the fraction ofrelatively high boiling point having the highest molecular weight. Incracking these individual fractions conditions are adjusted to produce aseries of cracked products having the same general relationship. Thus,the fractions of lower average molecular weight will have been crackedto produce a cracked material of lower average molecular weight thanwill have been produced from the parent fractions of relatively highermolecular weight. In this way the lighter constituents of the endproduct gasoline will have been predominantly produced from thosefractions of the cracking stock of lower molecular weight, whereas thosefractions of the gasoline of relatively higher molecular weight willhave been predominantly produced from the fractions of cracking stock ofrelatively higher molecular Weight.

I achieve a number of distinct advantages by this process, for example,the cracking is carried out on each of the individual cuts underconditions which may be predetermined in View of the rate ofdissociation of the particular stock to produce the optimum conversion,while the total number of dissociations or the degree of pyrogenesis toproduce any given yield of end product is relatively less than would benecessary with the indiscriminate cracking of a conglomerate stock, andthusthe concomitant losses in gas and/or tar or coke are greatlydiminished. A further distinct advantage is that polymerization to formproducts of a greater molecular weight than the parent stock does notoccur to the same degree as when cracking a conglomerate stock. It isunnecessary to carry the cracking reaction on some of the constituentsof the original stock to the point of forming polymers of a characterdeleterious to the operation of the process. Thus, in operating upon aconglomerate stock in the manner used at the present time it may beunavoidable to carry the cracking reaction to the point of third,fourth, fifth or higher scission. In the case of some of theconstituents of the initial charge and to the scission of polymerizedproducts formed therefrom in order to obtain the desired yield of theend product, whereas in my process I prefer to conne the reaction to theformation of the products of scission of a lower order. The scissions ofhigher order result in an increase in the products of decomposition, orpolymerization, which contributes to the formation of the products knownas tar and coke.

One of the preferred methods of operating my process is to crack eachindividual cut of the cracking stock to produce a cracked materialhaving an average molecular weight substantially half of that of theparent cut, for example, ranging from 75 to 25% of the average molecularweight of the parent cut. In this way, to an extent at least, with asingle decomposition of the various molecules composing the gas oilfraction, I am enabled to convert them into fractions of the gasolineseries, and by working upon a series of individual fractions I amenabled to produce an entire series of products boiling within thegasoline range with a minimum of individual molecular dissociations, orpolymerization. The conditions outlined may, of course, be varied inview of the particular stock or in view of the particularcharacteristics of the product desired,

as, for example, to produce a gasoline having a 75 certain definiteproportion of material boiling within a certain predetermined range.

The particular method of cracking the individual stocks may be any oneof the methods at present employed or hereafter developed. I may, forexample, crack these individual cuts in either liquid or vapor phase orin a combination of the two and under any degree of pressure. In apreferred embodiment of my invention, however, I subject the individualcuts to a vapor phase cracking oi relatively short duration ranging, forexample, from the order of one second up to times of the order of veminutes, at temperatures which may range between 750 and 1500 F. and atpressures which may range from a few atmospheres to partial vacuum. Inthis Way I am enabled to effect a carefully controlled dissociation ofthe individual stocks and accurately control the amount of dissociationapplied to each of these stocks so that a large proportion of theindividual cuts is subjected to a single dissociation, therebyautomatically throwing it into the boiling point range of the desiredend product with a minimum production of undesired products. A furtheradvantage of this procedure that Ihave discovered is that owing to therelatively short times involved, the temperature range in which crackingis effected and the low specic volume of the gases in the cracking Zone,the tendency to polymerization, or reformation of heavier products, isinhibited, the efficiency of the operation is increased and I am enabledto diminish the formation of tar and/or coke.

In determining the conditions under which in dividual cuts of theinitial conglomerate charging stock are to be cracked consideration mustbe given to the formation of fixed gas. I believe that the theory atpresent held that fixed gas produced by a cracking operation issubstantially produced by the cracking of tar to coke is mistaken andthat in fact such xed gas is substantially produced by the cracking ofconstituents falling within the gasoline range. I therefore so selectthe conditions of operation in the preferred form of my process as toprevent the cracking of such gasoline constituents, as, for example, byremoving them from the zone of reaction as quickly as possible. In thisrespect my process is radically different from those at presentpracticed in Which the products falling Within the gasoline range, orsome of them, are held in the zone of reaction for considerable periodsof time. In the processes in use at the present time these productswhich are extant in the Zone of reaction are either retained there byreason of the nature of the apparatus which does not permit of theirevacua tion immediately upon formation, or are retained there by reasonof their solution in liquid since they are in contact with large bodiesof heavier liquid content in the system. This effect is considerablyaggravated in many processes by the use of pressure. It Will be notedthat in my improved process because of the nature of the apparatus andthe charging stock used there is substantially no liquid present in thesystem at any time and the apparatus is such that products fallingwithin the gasoline range are removed substantially as quickly asformed.

The selection of the temperature bears a denite relation to the timeelement involved in the operation of the apparatus, the more rapid theevacuation of the products from the Zone of reaction the higher thetemperature which may be used, sufficient time being provided to permitthe reaction to take place. The effect of removing the products from thezone of reaction is to arrest the` reaction, and it may be desirable tocool immediately the products removed to prevent further reaction byreason of the contained heat.

My process will now be described with specific reference to theapparatus diagrammatically indicated in the drawings. Referringspecifically to Fig. l a cracking stock such as gas oil is passedthrough the tubular heater I, surrounded by the refractory setting 2,and heated by means of a burner such as 3 communicating with the settingthrough the port 4. Any alternative means of heating this stock to atemperature of complete or partial vaporization may be employed, such asa heat exchanger or a still. The partly vaporized cracking stock isdelivered through the pipe into the fractonating column 6. This columnmay be suitably insulated and provided with a number of rectifyingdevices such as the customary transverse partitions carrying down flowpipes and vapor contacting devices, not shown. The design of this columnis not a feature of the invention and any column or corresponding devicewhich is appropriately designed to separate petroleum oil into a numberof fractions by rectication may be alternatively employed. Provision ismade for taking off an over-head cut in vapor phase from the column bymeans of the vapor outlet 'I and a number of side cuts (ordinarily inliquid phase, but which may be in the vapor phase) from the side outlets8, 9, I0, Il, I2, I3, I4 and I5. The side cuts may be rected or strippedin a secondary rectifying column, if desired, to eliminate light ends,or, alternatively, any other means for obtaining an enhanced degree ofseparation may be employed. Any bottoms or heavy ends formed in thecolumn will be removed, preferably in a continuous fashion, by means ofthe bottom draw-01T I5A. The column may be supplied with cooling coilsadjacent to the top or intermediate points and with a heating coiladjacent to the bottom or with re-boiler sections at intermediatepoints. All such modifications will be incorporated to the degreenecessary to obtain the desired separation of the individual fractions.The cuts taken off through outlets 1 to I5, inclusive, are, in View ofthe necessities of practice, relatively close cut fractions having, forexample, 90% of constituents boiling within a 5 F. range, and whilethese ranges to some extent overlap, the cuts represent a completeseries of charging stocks, each of which approaches, Within the limitsof commercial practicability, an ideal charging stock as above defined.This series of cuts has a range of boiling points and correspondingmolecular Weights which increases throughout the series. These variouscuts are passed to individual crackers through control apparatuses It to23 inclusive which Will be here inafter more fully described, and fromthe control apparatuses the cuts pass respectively to the individualcracking apparatuses which have been diagrammatically indicated by thenumerals 24 to 3 I inclusive. I may employ any form of crackingapparatus, such as stills whichmay be adapted to operate under pressureor tubular crackers with or without reaction chambers or tubular stillsoperated .in the vapor phase. In any event, the

cracking is carried out under conditions which may be ascertained inadvance by tests to be suited to the individual cut. Preferably, whenoperating to make gasoline the individual cuts are cracked to such anextent that the average molecular weight of the cracked materialproduced from an individual cut ranges from 25 to 75% of that of the`parent fraction. I obtain in this Way a series of cracked products withserially larger molecular weights corresponding in order to themolecular Weights of the original fractions of cracking stock. Thedesired end product is therefore obtained by the selective cracking ofpreferred stocks and with less actual molecular disruptions andrecombinations than would be incidental to handling a cracking stock asa conglomerate. For convenience all of the cracked materials dischargedfrom the crackers 24 to 3|, inclusive, through outlets 32 to 39,inclusive, may be conducted by means of the manifold into the rectifyingcolumn 4| Which is of suitable construction to permit the separationthereof into the desired end product, as, for example, gasoline whichmay be taken oif in vapor phase, if desired, through the outlet 42, anda number of side cuts taken off through the side outlets 43 to 5|),inclusive. |Ihese side cuts taken off through the outlets 43 to 59,inclusive, are preferably fractionated so that 90% of the constituentsof each cut boil Within a range of F. and will be hereinafter more fullyconsidered. The column 6 may be operated under any pressure at whichappropriate fractionation may be secured, and for purposes of heateconomy, is preferably operated under a pressure in excess ofatmospheric, say, for example, a pressure not exceeding 100 pounds persquare inch. I achieve in this way the additional advantage that thecuts taken olf from the outlets 8 to l5, inclusive, may, in this manner,be supplied by virtue of their initial pressure to the respectivecracking apparatuses 24 to 3|, inclusive. The column 4| may be operatedunder pressure preferably less than that obtaining in column G so thatthe progress of material through the entire system is effected by virtueof the initial pressure obtaining in column 6. The side cuts from columnE fall within the gas oil range and are such as may, to a large extent,be converted into constituents boiling within the gasoline range,particularly where the cracking is so controlled as to produce moleculardisruptions occurring at or near the mid-point of the molecule.

The plant illustrated is only an approach to the ideal and somepolymerization may occur to products Whose molecular Weight is higherthan those taken oif through the side outlets 8 to l5, inclusive, ofcolumn 6. Such polymerized products are preferably separately processedas outlined in the preferred manner of processing the cut withdrawnthrough |5a, but for commercial reasons may be removed from column 4|through the side outlets 5| and diverted through pipe |5a to pipe |517to be combined with and processed with the products withdrawn fromcolumn 6 through outlet la.

The materials delivered through the pipe |51) represent materials whichcannot be converted into constituents of the gasoline series by a singledisruption adjacent the center of the molecule and, While I maysegregate these bottoms by fractionation in the manner described andthereafter crack selectively the individual components and thenrefractionate and then recrack the individual components falling withinthe gas oil range to gasoline range, I nd it suflcient to subject thesecomponents to a mild cracking by forcing the same through the tubularheater 52 surrounded, for example, by the refractory setting 53 heatedthrough the port 54 by means of the burner 55. 'Ihe cracking effected inthe heater 52 is not intended to convert the stock treated thereinpredominantly to gasoline, but rather to convert a substantialproportion of the stock into stocks having molecular Weightsapproximating those removed from column 6 through the side outlets 8 tol5, inclusive. There is, of course, the incidental production of a smallquantity of gasoline Where the operation is not accurately controlled.The stock cracked in this manner is delivered through the outlet 56 intothe rectifying column 5l, which may be of any suitable construction, inwhich it is fractionated to form an overhead distillate, for example,taken off through the outlet 58 Which may consist of gasoline and aseries of intermediate cuts taken off through the side outlets 59 to 86,inclusive, which are preferably cut to have 90% constituents boilingwithin a range of 50 F. These constituents boiling within the keroseneand gas oil ranges are such as may to a large extent be converted intoconstituents of gasoline by a single disruption occurring at or adjacentthe mid-point of the individual molecule. Any heavy ends may be takenolf through the side outlet S8, and, While they are preferably handledby separation and cracking of the individual segregates, as aboveoutlined, I und it suiicient in commercial practice to carry thesecompounds by means of the pipe t9 back into the inlet side of thetubular heater 5G for a second cracking operation. Any tarry productscollecting in the base of the towers 4|, 5l and Si are Withdrawn bymeans of bottom outlets 5Go, 'lil and lima, and diverted from thesystem. The products obtained from the side outlets 59 and 66 inclusive,represent products which have been cracked and separated into productshaving a molecular weight approximating those removed from the sideoutlets on column 6. As segregates they are passed through the controlapparatuses diagrammatically indicated by the numerals to I8, inclusive,discharging into cracking apparatuses 8| to 88,111- clusive, which maybe of any suitable construction, although they are preferably of thetype hereinafter described. The cuts obtained from tower 4l from theside outlets lil to 56, inclusive, are cuts which have been subjected tocracking and subsequent fractionation. These preferably will be crackedin the same manner as cuts 8 to l5, inclusive, derived from tower il,but for commercial reasons they may be blended with cuts 5e to 65,inclusive, and passed through the crackers 8| to 38, inclusive. In theideal embodiment of my process all polymerized cuts, even of the sainemolecular Weight as the cuts ll to i5, inclusive, will be treatedseparately. This is desirable for two reasons, the rst being that thedissociation speed of these polymers may be different than those of B tol5, inclusive, and further, because I have discovered that the presenceof polymerized cuts in contact With undecomposed cuts will enhance theformation of tar.

The cracking accomplished in these cracking apparatuses is conductedunder conditions ascertained by test or experience to be best for theparticular cuts and may be so adjusted as to produce cracked materialhaving an average molecular weight ranging from 25 to '75% of theaverage molecular Weight of the cut from which the cracked material isderived. In this way a series of cracked materials of serially largeraverage molecular Weight is produced which have been cracked underconditions conducive tc the maximum efficiency, under conditions socontrolled that the lighter parts of the end product,

for example, gasoline, are predominantly derived from the lighter cutsof cracked stock, whereas the heavier portions of the end product arepredominantly derived from the heavier portions of the cracked stock,and under conditions producing the minimum of fixed gas and polymerizedmaterial. The cuts which have been cracked through apparatuses 8| to 88,inclusive, may be diverted through the common iiow line 90 into therectifying column 9| which may be of any suitable design. From thisrectifying column gasoline may be removed through outlet 92. From theside of column 9| a series of cuts, shown as 83 to 99a, inclusive, maybe withdrawn and because of their small quantity may be diverted throughcrackers 8| to 88, inclusive.- It will be understood that if thepressure in, or the location of, the tower 9| is not such as to causeliquid to flow through the lines 93 to 89a, inclusive, into the linesleading to the cackers 8| to 88, inclusive, suitable pumps and checkvalves or other well-known apparatus may be employed for effecting thispurpose.

The cut may be diverted back to the tubular heater as in the case of cutas is the case likewise With cut 88 from column 51. The cut 88 differsfrom cuts |00 and 5| in that it represents to a large extent productswhich have not been `converted into those of the desired molecularweight, whereas cutsl5| and |00 are substantially products which havebeen formed by polymerization since the plant shown is only an approachto the ideal. For the same reason as before outlined, tarry matter maybe removed Y through line |00a.

Referring specifically to Fig. 2 which is the diagrammatic elevation ofapparatus adapted to processing crude oil or other petroleum oilscontaining constituents of higher boiling point than gasoline. Thecharging stock is passed through the tubular heater surrounded by thesuitable refractory setting 2, heated by means of the burnerdiagrammatically indicated at 3, communicating with the setting throughthe port 4.

.y The crude oil may be heated in heater I to a temperature ofsubstantially complete or partial vaporization and is thereafterdischarged through pipe 5 into the rectifying column 8. In the eventthat it is desired to produce a quantity of gas oil or cracking materialin addition to that normally occurring from the crude, conditions in thetubular heater may be adjusted to produce a cracking effect, preferablyof a moderate character, to convert heavier materials to a considerableextent into products such as kerosene and gas oil, which products are inturn susceptible to being converted into gasoline by a minimum number ofmolecular disruptions. This operation is not, of course, conducted underthe ideal cracking conditions which I have hereinabove described, but isutilized only as a matter of eX- pediency. The rectifying column 8 maybe of any suitable type. Provision may, for example, be made to take anoverhead cut of gasoline by means of the vapor outlet 1 and a series ofside cuts from the outlets 8 to l5, inclusive, and ||5 to ||8,inclusive. It will, of course, be understood that any alternative numberof side cuts may be employed, the design in any case being determined bythe character of the stock to be treated and the number of side cutswhich it is desired to make. Assuming that cuts such as kerosene and gasoil are taken off from the side outlets 8 to l5, inclusive, these arepreferably fairly closely fractionated so that 90% of the totalconstituents of each cut will boil within a range of say 50 F. Productsevolved from the tower 8 which are heavier than gas oil, or so heavythat they cannot be converted into gasoline to a large extent by asingle disruption adjacent the mid-portion of the molecule, may be takenoff from the column 8 by means of the side outlets l5 to |8, inclusive,combined in the manifold ||5a and thereafter treated in the same manneras the products obtainedfrom the outlet |5a of Fig. 1. Any heavy residueresulting during the operation may be diverted from the system by meansof the outlet |20.

The several side cuts taken from column 6 through the side outlets 8 toI5, inclusvamay be handled in the identical manner as the side cutstaken from column 8 of Fig. 1 through the side outlets 8 to i5,inclusive, and inasmuch as the product taken from the column 8 throughthe side outlets ||5 to H8, inclusive, is handled in the identicalmanner as the products taken from the column 8 in Fig. l through thepipe |5a, the subsequent progress of these materials may be ascertainedby reference to the previous description relating to Fig. 1 and need notbe more fully illustrated or described.

Referring specifically to Figs. 3 and 4, the form of cracking apparatuswhich I prefer to employ for cracking the individual closelyfractionated cuts which have been described from time to time isdetailed, which apparatus has been designated for example by numerals 24to 3|, inclusive, and 8| to 88, inclusive. This apparatus consists of arefractory setting |50 and may be heated through the port |5| by meansof the burner diagrammatically indicated as |52. A baiile wall such as|53 may be provided and a down draft section |54 communicating with astack |55. The tubular heaters |58 and |51 in the down draft section maycomprise a number of tubes through which oil may circulate by means ofinlets and outlets |58, |58, |88, |8I, respectively, and sections ofthis character may be utilized for heating or cracking the cuts ofrelatively wide boiling point corresponding to the operations which havebeen previously described as conducted in tubular heaters 52. The Wallsof the setting |50 are'preferably lined with a number of relativelyshort tubular heaters |82 to |11, inclusive, each of which is adapted tothe circulation of hydrocarbon materials by means of inlets and outletssuch as |8811 and |681), etc. These sections are relatively short beingcomposed of only a few lengths of tubing adapted to be heated to a largeextent by the radiant products of combustion evolved. In operation Iprefer to maintain these heaters |82 to |11, inclusive, at temperaturesintermediate between 750 and 1500 F. and to conduct cracking operationstherein at relatively low pressures ranging from a few atmospheres tosub-atmospheric. The total time of heating of the hydrocarbon gases atthese temperatures is preferably limited to a period ranging from onesecond up to the order of ve minutes, which conditions I find to favor asymmetrical dissociation which is amenable to control with asimultaneous forma tion of a relatively small quantity of the prode uctsof re-association or polymerization. In vapor phase cracking apparatus,such as that Shown, I may admix with the petroleum oil undergoingcracking in the vapor phase a material to limit the formation ofpolymers. I have discovered the formation cf polymers is inuenced, amongother things, by the concentration of the spondingly controlled.

unsaturates produced by decomposition per unit of space and that thisconcentration and consequent polymerization may be inhibited or limitedby admixing with the petroleum oil a substance which does notdeleteriously affect the cracking reaction. In vapor phase reactions Iprefer to use a material which is gaseous at the temperature ofoperation, such as a Xed gas, steam, carbon dioxide, hydrogen, etc. Allsuch substances which are not petroleum oils undergoing cracking andwhich do not deleteriously aiect the cracking reaction, will behereinafter referred to as diluent gases. The cracked and heatedhydrocarbons delivered through the respective outlets of coils S2 toil?, inclusive, are preferably quenched by cooling them immediatelyeither by Contact with a liquid or a vapor at temperature beloyvicracking, for example, by contact with steam or by conducting themagainst relatively cool metal surfaces, for example, through arelatively cool large exchanger. I am thus enabled to control the extentto Which the reaction is permitted to proceed and thus determine theconstitution of the product. The combination, rectiiication andsubsequent disposition of these products has been hereinabove described.

Referring speciiically to Fig. 5, this is a diagrammatic representationof control apparatus which has been indicated by the numerals i6 to 23,inclusive, and i to '18, inclusive. rIhis apparatus comprises the sideoutlet, such as carrying a fraction from any one of the rectifyingcolumns hereinabove described, discharging into cracking apparatus suchas diagrammatically indicated by the numeral 2li. A cooling coil such as2t@ is connected into the outlet 8, preferably adjacent the under sidethereof. This coil, controlled by the valve 2M, discharges into the pipe8 at a point belowits origin. The coil 2% may be surrounded by areceptacle, such as 202, through which a cooling fluid is circulated bymeans of inlets and outlets, such as 293 and 2M, respectively, so thatany petroleum oil, either in liquid or vapor form., passing through thecoil G is automatically cooled and discharged in cooled condition backinto pipe 8. By manipulation of the valve 23E the amount of cooledmaterial which is reintroduced into the pipe 8 may be carefullycontrolled, and in this way the temperature of the products passing intothe cracking apparatus 2 may be controlled, and hence the temperature ofthe products discharged from the cracking apparatus Eil may be corre-'Ihe form of apparatus which I have just described is particularlyadapted to the close control of vapor phase cracking, which I prefer toconduct in apparatus such as 24 and to which I prefer to subject thevarious fractions into which I separate my original cracking stock.

I claim:

1. The process of treating hydrocarbon oil Which comprises dividing saidoil by distillation into a plurality of hot fractions heavier thangasoline and having different boiling ranges, passing said fractionsWhile hot through individual confined paths in a common heating zone,supplying sufcient heat to said heating zone to raise said fractions tothe desired cracking temperature, counteracting any variations from saiddesired cracking temperature by cprrectively adjusting the temperatureof the several hot fractions, prior to their introduction into saidconfined paths, combining the resulting cracked products and separatingtherefrom gasoline of the desired characteristics.

2. The process of treating hydrocarbon oil for the production ofgasoline, which comprises producing a plurality of separate hot bodiesof hydrocarbon oil, passing separate streams of oil from said bodies inindividual confined paths through a common heating Zone, supplyingsufcient heat t0 said common heating zone to raise said streams of oilto the desired cracking temperature, removing the resulting crackedproducts and forming a desired blended gasoline distillate therefrom,and selectively cooling said streams of oil prior to their introductionto said common heating zone, to such a ratio that during theirsubsequent passage through said heating zone said streams of oil undergocracking to substantially the desired extent.

3. The process of forming a plurality of highly heated bodies of oil,which comprises establishing a plurality of individual quantities of oilat elevated temperatures less than those desired for said bodies of oil,cooling certain of said quantities of cil with respect to other of saidquantities of oil, then passing said quantities of oil at theirrespective resulting temperatures in a plurality of individual streamsthrough a common heating zone wherein each stream is subjected to heatfrom the same source as each of the other streams and is thereby raisedto a desired high temperature, and correcting any undesired variation insaid high temperature by controlling the cooling step mentioned so thatthe bodies of oil emerging from said individual streams have the desiredindividual temperatures.

PERCY C. KEITH, JR.

